What is the proper betting procedure with 7 players after the first three players go all in before preflop?

Question

             Blinds are 300/600 in this game. Texas Hold'em No Limit., Seven players

1. Player "A" first to bet goes all-in with a 600 + 150 raise for a total of 750.

2. Player "B" second to play goes all-in with 600 + 50 raise for a total of 650.

3. Player "C" third to play goes all-in with 600 + 300 raise for a total of 900.

4. My question is; What is the proper bet for player "D" to call and raise a MINIMUM raise bet?

     Is it the 600 + 600 for a total of 1200?       or
     Is it the 900 from player "C" + minimum raise of 600 for a total of 1500?     
   

5. Players "E" and "F" have yet to play.

Answer 1

Outside of casino-specific rules, this follows the standard full minimum raise rule for big bet Holdem.

Legal raises (all-in) below the minimum are treated as calls, although players to act face a different bet size than previously. Therefore, a minimum raise by player D presumed to have more than 1200 chips behind, is 1200.

If player C were to go all-in for 1199 total, player D could make a legal non-all-in raise to 1200, and player E would still have the option to raise. This seems strange at first, but a raise here is practically the same as a call, both of which retain open action, so the difference is only a technical one. Furthermore, such a raise is seldom advantageous to the raiser, as it tends to offer favorable odds to players yet to act.

EDIT: I haven't found a "Holdem Rules" that outlines this interpretation with more specificity than "What is a minimum raise?" However, some time ago I wrote this logic into a poker engine and verified against existing poker sites, to answer the question: Does a raise over a non-minimum raise go on top of the new facing bet, or does it go on top of the last minimum-qualifying bet? The answer is the latter.